In industry nowadays, success or failure depends in part upon knowing the up-to-date status of various assets. For example, in the freight delivery business, up-to-date knowledge of the location and, in some instances, the environment of various assets, such as pallet goods, is critical to efficient and reliable operations. Failure to maintain up-to-date status information can result in temporarily lost assets, sub-optimal use of the assets, and in the case of freight delivery, missed or late deliveries.
Recently, technologies have been developed that greatly assist in tracking locations of assets. Radio frequency identification (RF or RFID) systems have been developed in which transmitter devices, often referred to as “tags,” wirelessly communicate with readers. RF tracking systems are typically used in parcel tracking and sorting, container tracking, luggage tracking, retail tracking, warehouse tracking and inventory operations. The RF transmitter devices may be either passive or active. Passive devices absorb signals transmitted by the reader and retransmit their own signals, such as identification information. While passive transmitter devices do not require a local energy source, their resulting transmit range is relatively short, typically less than 5-10 meters. In contrast, active transmitters, which send a signal to indicate their location, include a local energy source (such as a battery) that improves transmission range. Depending on the wireless signal system used by the device, the range may be on the order of several meters or several hundred meters. Regardless of the types of transmitter device used, knowledge of the fixed location of the reader device allows users to identify the location of the asset that has a tracking device attached thereto.
Active tag systems are preferred for some applications due to their long range transmission range. Unfortunately, the position signal or date “ping” drains battery life of the transmitter device, thus resulting in added operational cost of the system, due to needed recharging or replacement of the battery.